1. Field of the Invention
The present invention relates to an image forming apparatus for use in a digital copying machine having a laser printer coupled to a scanner.
2. Description of the Related Art
Recently, digital copying machines (image forming apparatuses) put to practical use have a laser printer (image forming unit) for forming an image by an electrophotographic system, coupled to a scanner (image reading unit) for reading image data of an original as image data by moving an optical carriage (scanning means).
These types of copying machines are designed to form an image only at the time the optical carriage of the scanner moves in its forward direction. This is because also forming an image during the return movement of the optical carriage requires:
the order of reading image data by means of an image sensor disposed in the optical carriage is reversed;
the position control of the optical carriage along the subscanning direction should be executed at a high accuracy;
complex synchronization of the printing operation of the printer with the scanning operation of the scanner must be executed; and so on.
A laser printer itself is originally designed to be able to form an image at a high speed (high-speed printing) if it receives image data in rapid succession. Since a scanner involves the return operation of the optical carriage which does not contribute to image forming, however, the time required for this return operation is a bottleneck in sufficiently improving the image forming speed of a printer. With the above in mind, there is a demand for an image forming apparatus free of problems.